They obtained this information by "secret photography, infiltration or tailing after someone", it said.

"Based on the information, the couple compiled so-called 'reports' and sold them at high prices to their clients, most of which are China-based multinational corporations, including GSK China," it said.

Local courts "will hold [a] hearing about the case soon", the agency added.

'Learning lessons'

In a statement earlier this month, GSK said that its China operation hired ChinaWhys in April 2013 "to conduct an investigation following a serious breach of privacy and security related to the company's China general manager".

This is understood to relate to a sex tape said to have shown the general manager, Mark Reilly, who said the footage was filmed without his knowledge or consent.

The video was sent to GSK's London-based CEO Andrew Witty with an email accusing Mr Reilly of being behind systematic corruption in the company's China operation.

GSK suspected a former senior staff member, Vivian Shi Wen, who was dismissed at the end of 2012, had sent the email. ChinaWhys was also asked to find out how the video had been filmed and who was behind it.

Ms Shi has previously denied being the GSK whistleblower. Attempts by the BBC to reach her have been unsuccessful.

Mr Reilly is currently being investigated by Chinese authorities, as are at least two other senior GSK China executives. He is alleged to have pressed his sales team to bribe doctors, hospital officials and health institutions to increase sales of GSK products.

He is currently effectively detained in China, and has made no recent comment.

GSK has described the allegations as "deeply concerning".

"We are learning lessons from this situation and we are determined to take all actions necessary as a result," it said in the statement.